Cascade refrigeration system with refrigerant bypass

ABSTRACT

A cascade refrigeration system for installation where the machinery of the system is remote from the cooled space, in which an insulated bypass conduit withdraws at least some of the refrigerant available at the cooled space under a low-load condition, and delivers this refrigerant to a condenser in one of the stages, thus maintaining the circulation of refrigerant.

United States Patent Inventor Mark W. Brigs Holland, Mich.

Appl. No. 830,027

Filed June 3, 1969 Patented July 6, 1971 Assignee Thermotron Corporation Holland, Mich.

CASCADE REFRIGERATION SYSTEM WllTH IREIFMG'ERANT BYPASS 3 Clatiims, No Drawings U.S.Cl 62/197,

Int. Cl .Q... F25b41/00 Field of Search 62/ l 96,

[56] References Cited UNITED STATES PATENTS 2,680,956 6/1954 Haas t t t i 62/335 Primary Examiner-Meyer Perlin I Att0mey-Glenn B. Morse ABSTRACT: A cascade refrigeration system for installation where the machinery of the system is remote from the cooled space, in which an insulated bypass conduit withdraws at least some of the refrigerant available at the cooled space under a low-load condition, and delivers this refrigerant to a condenser in one of the stages, thus maintaining the circulation of refrigerant.

PATENTED JUL-6 new MARK W. BRIGGS i! N VENTT )R AHy.

CASCADE ltlEll RllGlEhArllllON SYSTEM Wll'illir' REFREGEIRANT BYPASS BACKGROUND OF THE lNVENTlON The so-called cascade refrigeration system is frequently used where relatively low temperatures in the controlled en vironment are desired. This arrangement usually involves an installation of evaporator coils in the controlled chamber, supplied with refrigerant by a conventional compressor-con denser system. The compressor receives the refrigerant in gaseous form from the evaporator, compresses it, and the heat of compression is removed by the condenser before returning the refrigerant in liquid form again to the expansion valve ahead of the evaporator. in the cascade arrangement, a second stage is used to cool the first stage condenser. The output of the compressor-condenser system of the second stage is passed through an expansion valve, and is delivered to the condenser in heat-exchanging relationship with the output of the first stage compressor. Such an arrangement is well established refrigeration technique, and a number of stages in cascade relationship may be incorporated, if necessary.

There are a number of situations in which it becomes desira ble to have a considerable distance between the compressorcondenser system and the controlled chamber. Where a central installation of refrigeration machinery is to supply a number of controlled chamber units, this remote relationship becomes a practical necessity. A problem arises, however, in that the delivery of the refrigerant from the first stage condenser to the evaporator in the controlled chamber over long distances has a tendency to cause the refrigerant to pick up sufficient heat to produce sections of refrigerant in gaseous form within the conduit. This is particularly true when the velocity of flow within the conduit is interrupted because of the interruption in the requirements of the evaporator. When the controlled chamber is down to the required temperature for the moment, the flow of refrigerant is either interrupted entirely, or sufficiently reduced in velocity to increase the problem of heat pickup. Where gaseous inclusions in the liquid line are present, the next cooling cycle will require that the entrapped gas in the liquid line will have to be pulled through the expansion device associated with the evaporator before refrigeration can begin. This lag in obtaining refrigeration causes cycling of the controlled temperature, and an improper balance in the primary refrigerant pressures.

SUMMARY OF THE lNVENTlON This invention eliminates the possibilities of stagnation in the first stage liquid line by providing a bypass for the refrigerant at a point adjacent the first stage evaporator. During periods in which the refrigeration requirements of the evaporator are either reduced or nonexistent, a control valve responsive in some way to these temperature conditions diverts the refrigerant through an expansion device into an insulated conduit leading baclc to some convenient point on the first or second stage compressor condenser system where this cooled refrigerant may be utilized to withdraw waste heat. Preferably, this point is between the second stage compressor and the conventional condenser associated with the output of that compressor.

The result of this arrangement is to maintain a constant flow of liquid refrigerant in the supply line to the remote evaporator, which eliminates the danger of heat pickup. By the addition of this insulated line as a third pipe in conjunction with the conventional two-pipe system, runs of a hundred feet or more are perfectly feasible. Test data and computations pro vide assurance that runs conceivably as long as 300 feet are entirely practical.

DESCRIPTION OF THE DRAWING The drawing presents a schematic diagram of a typical twostage cascade refrigeration system incorporating the present invention.

DESCRIPTKON OF THE PREFERRED EMBODIMENT The equipment located within the dotted rectangle it) on the schematic diagram is associated with a remote chamber in which the temperature is controlled by the evaporator coils ill. These coils receive refrigerant from the distributor 112, after it has passed through the expansion device 13. Flow of refrigerant within the coils llll is controlled by the temperature needs within the associated chamber by a detector line such as the conduit M, to which the expansion valve 113 is responsive. Refrigerant flow through and around the expansion valve 13} is controlled by the combined action of the flow control 15 and the liquid solenoids id and lll'. The evaporated refrigerant gas from the coils ill is received by the return conduit lll, through which the refrigerant is delivered back to the first stage compressor 319 through the suction fiter 2i) and the vibration eliminator Ell. An injection expansion valve 22 may be incorporated in the circuit, if desired, being supplied with liquid refrigerant by the line 23 communicating with the liquid line 24; delivering liquid refrigerant to the remote unit ill. The service valve 25, the vapor tank as, the relief valve 27, and the purging valve 28 are standard installations in this type of system. A regulator valve 29 and a dump valve Iill are also preferably incorporated, with the dump valve being actuated by pressure conditions communicated through the line M.

The output of the first stage compressor is delivered through the discharge service valve 32 and the discharge vibration eliminator 33 and the pumpdown valve M to the oil separator 3b. The refrigerant then passes through the line so to the condenser 37. Liquid refrigerant then proceeds through the filter dryer 38 and the liquid line 39 back to the remote unit lltl. Oil extracted by the separator 35 is returned to the compressor through the line th and the oil filter 4. 11.

The second state compressor 42 delivers compressed refrigerant through the discharge service valve 43 and the vibration eliminator M to the water-cooled condenser 55. The control valves 46 and i? are preferably incorporated in the system. A water-regulating valve 4% is provided in the watersupply line H2, and a relief valve should also be present. Condensed refrigerant from this section of the second stage is carried by the conduit 5i through the filter dryer 52, the liquid indicator b3, and the liquid solenoid 54 to the expansion valve This valve is controlled by the detector line 56, and delivers expanded refrigerant to the distributor 57. This expanded refrigerant is applied in heat-exchanging relationship to the compressed refrigerant of the first stage by the condenser 37. Spent refrigerant from the condenser 37 is returned through the line 5d, the suction filter $9, the vibration eliminator so, and the service valve st to the second stage compressor. An additional element in the two-stage system may be the water-cooled desuperheater or installed in heat-exchanging relationship with the output of the first stage compressor. The water lines 453 and till provide the cooling circuit controlled by the valve regulator as responsive to temperature conditions in the line 36. The water line 49 may be considered as the pressure source, with the line so functioning; as the return.

The description to this point has summarized a relatively standard cascade refrigeration system within which the present invention may be incorporated. The arrangement for maintaining a constant flow of liquid refrigerant in the line 24 centers in the provision of the bypass circuit which includes an insulated conduit s7 receiving the output from the expansion valve as controlled as a function of conditions in the evaporator coils ll communicated by the line 69. Liquid refrigerant is supplied to the expansion valve till by the bypass supply line 7% communicating with the liquid line is at a point adjacent or within the remote unit W. The liquid diverted through the expansion valve 68 passes through the liquid solenoid 71. The expanded refrigerant from the valve as is conducted back to the bypass heat exchanger 72 through the insulated line 67, and this refrigerant is returned from the bypass heat exchanger to the input of the first stage compressor by the return line '73. Waste heat from the output of the second stage compressor is therefore removed from the refrigerant of that stage by the condenser 72, which would otherwise have to be removed by the water-cooled condenser 45. The supply of water can therefore be reduced as a result of the utilization of this source of cooling. The various valves and other control devices may be set in such a manner as to maintain a continuous flow of refrigerant in the liquid line 24, which is either supplied to the coils 11, or diverted through the bypass line 67. The use of a bypass, per se, in a refrigeration system of a different type, and for different purposes, has been noted in the R. E. Gould et al. US. Pat. No. 2,332,71 l.

I claim:

1. A cascade refrigeration system including a first stage having a compressor, a remote heat-absorbing evaporator unit, and a condenser, and also including a second stage having a compressor and a condenser, and including conduit means connecting the output thereof with said first stage condenser, said first stage having a liquid conduit extending from said condenser unit to said first stage evaporator unit, and a return gas conduit extending from said first stage evaporator unit to the input of said first stage compressor, wherein the improvement comprises:

a bypass circuit communicating with said liquid conduit at a point adjacent said first stage evaporator unit, and including a control valve adjacent said point and responsive to temperature conditions associated with said first stage evaporator unit and adapted to divert refrigerant into said bypass circuit, said circuit also including expansion means, a bypass heat exchanger in heat-exchanging relationship with the output of one of said compressors, a heat-insulated conduit extending from said expansion means to said bypass heat-exchanger, and a return conduit extending from said bypass heat exchanger to a point communicating with the input into one of said compressors.

2. A system as defined in claim 1, wherein said bypass return conduit communicates with the input of said first stage compressor.

3. A system as defined in claim 1, wherein said bypass heat exchanger is disposed with the output thereof connected to the input of said first stage condenser. 

1. A cascade refrigeration system including a first stage having a compressor, a remote heat-absorbing evaporator unit, and a condenser, and also including a second stage having a compressor and a condenser, and including conduit means connecting the output thereof with said first stage condenser, said first stage having a liquid conduit extending from said condenser unit to said first stage evaporator unit, and a return gas conduit extending from said first stage evaporator unit to the input of said first stage compressor, wherein the improvement comprises: a bypass circuit communicating with said liquid conduit at a point adjacent said first stage evaporator unit, and including a control valve adjacent said point and responsive to temperature conditions associated with said first stage evaporator unit and adapted to divert refrigerant into said bypass circuit, said circuit also including expansion means, a bypass heat exchanger in heat-exchanging relationship with the output of one of said compressors, a heat-insulated conduit extending from said expansion means to said bypass heatexchanger, and a return conduit extending from said bypass heat exchanger to a point communicating with the input into one of said compressors.
 2. A system as defined in claim 1, wherein said bypass return conduit communicates with the input of said first stage compressor.
 3. A system as defined in claim 1, wherein said bypass heat exchanger is disposed with the output thereof connected to the input of said first stage condenser. 